No, the data does not expire.
Your jobs and all of their contents (appointment logs, notes, estimates, invoices, photos, etc.) will be available for as long as your Cinderblock account remains active. No matter how old the job is, your team will be able to access the information.
If you downgrade to a lower tier plan, you may lose visibility to data which relies on a higher-tier feature. But don’t worry, your data is not lost, you can upgrade any time to regain access to affected info.